Summary: Implementation is a little crazy but this seems to work as advertised.
Test Plan: Acquired locks with "lock.php". Verified they held as long as the process reamined open and released properly on kill -9, ^C, etc.
Reviewers: nh, jungejason, vrana, btrahan, Girish, edward
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T1400
Differential Revision: https://secure.phabricator.com/D2864
